2006 Vol. 14, No. 3

论文
Based on the measured data in the field and according to the form and energy of soil water,the mechanism of the rainfall infiltration in the surface of the granite forestland of Three Gorges area was studied.The results showed that when the rainfall intensity was larger than soil infiltration rate and soil water did not reach the largest capillary water volume,preferential flow appeared.It appeared earlier than infiltrated soil water flow.When the rainfall intensity was smaller than soil infiltration rate,and there was no water accumulated in the surface,infiltrated soil water flow appeared earlier than preferential flow.From the flow process of infiltrated soil water,it can be seen that the infiltrated soil water flow appeared earlier than the preferential flow when there was no water accumulated in the surface,and that the preferential flow appeared earlier than the infiltrated soil water flow when there was water accumulated in the surface and the soil water did not reach the biggest capillary water volume.In both conditions,the peak of preferential flow appeared earlier than that of infiltrated soil water flow. Based on the measured data in the field and according to the form and energy of soil water,the mechanism of the rainfall infiltration in the surface of the granite forestland of Three Gorges area was studied.The results showed that when the rainfall intensity was larger than soil infiltration rate and soil water did not reach the largest capillary water volume,preferential flow appeared.It appeared earlier than infiltrated soil water flow.When the rainfall intensity was smaller than soil infiltration rate,and there was no water accumulated in the surface,infiltrated soil water flow appeared earlier than preferential flow.From the flow process of infiltrated soil water,it can be seen that the infiltrated soil water flow appeared earlier than the preferential flow when there was no water accumulated in the surface,and that the preferential flow appeared earlier than the infiltrated soil water flow when there was water accumulated in the surface and the soil water did not reach the biggest capillary water volume.In both conditions,the peak of preferential flow appeared earlier than that of infiltrated soil water flow.
There have been two mechanical models for the failure criteria of bending deformation in the rock slope with dip direction opposite to the dip direction of the rock strata.The models are developed using the elastic buckling model of averticam compressive bar and the bending cracking model of a horizontal beam.Whereas,some important factors,such as the additional bending moment induced by the deflection and the slipping resistance on the interface of rock layers are not considered.In this paper,based on the mechanical analyses of the anti-dip rock layers,a model of the slanting elastic cantilever beam with fixed bottom and freeuop boundary and equal thickness is established,in which the slipping resistance on beams side face is taken into account.Rayleigh-Ritz energy method was introduced to develope the critical conditions of the elastic buckling of the beam and the bending fracture of the fixed bottom.The application in real case analyses and the discussions afterwards indicate that the elastic buckling model is applicable in very steep rock stratum,and that the bending fracture is the deforming and failure mechanism of median steep to steep anti-dip layered slope.Furthermore,the critical conditions of bending fracture is significantly influenced by the mechanical properties of the interface between layers. There have been two mechanical models for the failure criteria of bending deformation in the rock slope with dip direction opposite to the dip direction of the rock strata.The models are developed using the elastic buckling model of averticam compressive bar and the bending cracking model of a horizontal beam.Whereas,some important factors,such as the additional bending moment induced by the deflection and the slipping resistance on the interface of rock layers are not considered.In this paper,based on the mechanical analyses of the anti-dip rock layers,a model of the slanting elastic cantilever beam with fixed bottom and freeuop boundary and equal thickness is established,in which the slipping resistance on beams side face is taken into account.Rayleigh-Ritz energy method was introduced to develope the critical conditions of the elastic buckling of the beam and the bending fracture of the fixed bottom.The application in real case analyses and the discussions afterwards indicate that the elastic buckling model is applicable in very steep rock stratum,and that the bending fracture is the deforming and failure mechanism of median steep to steep anti-dip layered slope.Furthermore,the critical conditions of bending fracture is significantly influenced by the mechanical properties of the interface between layers.
This paper presents a stability assessment of the landslide occurred at Hanali.The field geological investigation has shown that the Hanali landslide was composed of nine parts.The characteristics and classification of each of the nine landslide parts were studied.On the basis of the field investigation,a theoretical stability assessment of the Hanali landslide is carried out according to the stability coefficients.The stability coefficient is deduced in this paper. This paper presents a stability assessment of the landslide occurred at Hanali.The field geological investigation has shown that the Hanali landslide was composed of nine parts.The characteristics and classification of each of the nine landslide parts were studied.On the basis of the field investigation,a theoretical stability assessment of the Hanali landslide is carried out according to the stability coefficients.The stability coefficient is deduced in this paper.
Stability of high rock cut slope is a complicated systematic project,which relates to the engineering geology,rock mechanics,and computation science,etc.On the basis of carefully studying the geological background and environmental conditions,systematic analysis and evaluation,comprehensive integration method are the best method for effective analysis,research and solution of this problem.For the case of Zhang-Long expressway Shi Kongshan No.Ⅱ section high rock slope,on the basis of the systematic analysis of engineering geologic properties,Stereographic polar projection method,and Finite Element Method(FEM) are used in comprehensive evaluation and systemic analysis,by which the slope stability results are obtained,and then are accepted and adopted by design and construction corporations.The slope has already kept in safe operation for several years after its completion which shows that this comprehensive evaluation and systemic analysis are successful and effective,and can be an important pathway of stability evaluation of high rock slope.Its comprehensive contents and integrated mode and its perfection and engineering practicability need further research,engineering practice and experience accumulation. Stability of high rock cut slope is a complicated systematic project,which relates to the engineering geology,rock mechanics,and computation science,etc.On the basis of carefully studying the geological background and environmental conditions,systematic analysis and evaluation,comprehensive integration method are the best method for effective analysis,research and solution of this problem.For the case of Zhang-Long expressway Shi Kongshan No.Ⅱ section high rock slope,on the basis of the systematic analysis of engineering geologic properties,Stereographic polar projection method,and Finite Element Method(FEM) are used in comprehensive evaluation and systemic analysis,by which the slope stability results are obtained,and then are accepted and adopted by design and construction corporations.The slope has already kept in safe operation for several years after its completion which shows that this comprehensive evaluation and systemic analysis are successful and effective,and can be an important pathway of stability evaluation of high rock slope.Its comprehensive contents and integrated mode and its perfection and engineering practicability need further research,engineering practice and experience accumulation.
The incompetent structural plane was actually a combination of two mediums: medium 1 is elasto-brittle or strain-hardening material and medium 2 was strain-softening material,because it has different attribute in different environment or different parts.A cusp catastrophe model is presented to describe the behavior of sliding along one deep incompetent structural plane of a gravity dam foundation,and the sufficient conditions leading to instability are discussed.It is found that the instability of sliding relies mainly on the stiffness ratio k,the homogeneity index of the medium m and the geometry-mechanic parameter and that the reliability of the traditional limit analysis method is deficient.The influence of water fluctuation and prevention project is discussed too.It is indicated that the rising of water of the reservoir enlarges the material homogeneity and hence reduces the stiffness ratio k and that the instability of the dam may be posterior to the time when water comes to its peak.The prevention project enhances the potential of anti-sliding,and also has a new effect on enlarging the stiffness ratio k,which makes the instability of sliding occur more difficultly. The incompetent structural plane was actually a combination of two mediums: medium 1 is elasto-brittle or strain-hardening material and medium 2 was strain-softening material,because it has different attribute in different environment or different parts.A cusp catastrophe model is presented to describe the behavior of sliding along one deep incompetent structural plane of a gravity dam foundation,and the sufficient conditions leading to instability are discussed.It is found that the instability of sliding relies mainly on the stiffness ratio k,the homogeneity index of the medium m and the geometry-mechanic parameter and that the reliability of the traditional limit analysis method is deficient.The influence of water fluctuation and prevention project is discussed too.It is indicated that the rising of water of the reservoir enlarges the material homogeneity and hence reduces the stiffness ratio k and that the instability of the dam may be posterior to the time when water comes to its peak.The prevention project enhances the potential of anti-sliding,and also has a new effect on enlarging the stiffness ratio k,which makes the instability of sliding occur more difficultly.
Surrounding rock-mass stability of underground engineering under complex geological conditions has been one of the hot topics for engineering geologists.This paper presents a case study of a double-arch tunnel Manxie No.4,one of Simao-Xiaomengyang expressway tunnels,encountered an extremely complicated geological structure.The authors simulated the dynamic constructional response of a shallow-buried and unsymmetrical-loaded double-arch tunnel across ancient landslide,including press field,displacement field and plastic zones in surrounding rock-mass.In addition,locations of stress concentration and potential failure zones are clearly delineated in rock-mass,which will not only provide information needed for guiding the construction of the tunnel,but also establish valid theoretical evidence for optimal design of the tunnel.At the end,the authors emphasize that complete treatment of whole ancient landslide and sufficient reinforcement of partition wall should be taken to ensure stability of surrounding rock-mass and safety of the whole double-arch tunnel. Surrounding rock-mass stability of underground engineering under complex geological conditions has been one of the hot topics for engineering geologists.This paper presents a case study of a double-arch tunnel Manxie No.4,one of Simao-Xiaomengyang expressway tunnels,encountered an extremely complicated geological structure.The authors simulated the dynamic constructional response of a shallow-buried and unsymmetrical-loaded double-arch tunnel across ancient landslide,including press field,displacement field and plastic zones in surrounding rock-mass.In addition,locations of stress concentration and potential failure zones are clearly delineated in rock-mass,which will not only provide information needed for guiding the construction of the tunnel,but also establish valid theoretical evidence for optimal design of the tunnel.At the end,the authors emphasize that complete treatment of whole ancient landslide and sufficient reinforcement of partition wall should be taken to ensure stability of surrounding rock-mass and safety of the whole double-arch tunnel.
Shiliushubao landslide is an important part of Huanglashi landslide group,one of the largest landslides in three gorges.It is located on the north bank of Yangtze river,1.5 km east of Badong sity and 66 km upstream of three gorges dam.The displacement of the landslide became more and more visible in 1970s,has become especially apparent since the reservoir impounding.Based on the geomorphy,geology,and deformation-failure features of Shiliushubao landslide,as well as the slope movement monitoring dada of more than 10 years,the influence factors and the deformation development process are studied.The deformation development tendency was predicted by using the GM(1,1) model.This paper provides some useful data for the measures of landslide prevention and the design of landslide treatment. Shiliushubao landslide is an important part of Huanglashi landslide group,one of the largest landslides in three gorges.It is located on the north bank of Yangtze river,1.5 km east of Badong sity and 66 km upstream of three gorges dam.The displacement of the landslide became more and more visible in 1970s,has become especially apparent since the reservoir impounding.Based on the geomorphy,geology,and deformation-failure features of Shiliushubao landslide,as well as the slope movement monitoring dada of more than 10 years,the influence factors and the deformation development process are studied.The deformation development tendency was predicted by using the GM(1,1) model.This paper provides some useful data for the measures of landslide prevention and the design of landslide treatment.
This paper presents test results of sand liquefaction under sinusoid loading at a site of one Changde-Zhangjiajie expressway bridge using the DSD-160 electric-magnetic vibration triaxial apparatus.A new method for evaluating sand liquefaction based on dynamic triaxial apparatus is proposed in combination with an earthquake shear stress time history method.The results show some clear evidences for the potential sand liquefaction under earthquake ground motion with different exceedance probability.A risk classification is also given.These results not only prove the feasibility of the new approach on evaluation of sand liquefaction,but also help to gain a better understanding of the seismic resistance design before the construction of the bridge. This paper presents test results of sand liquefaction under sinusoid loading at a site of one Changde-Zhangjiajie expressway bridge using the DSD-160 electric-magnetic vibration triaxial apparatus.A new method for evaluating sand liquefaction based on dynamic triaxial apparatus is proposed in combination with an earthquake shear stress time history method.The results show some clear evidences for the potential sand liquefaction under earthquake ground motion with different exceedance probability.A risk classification is also given.These results not only prove the feasibility of the new approach on evaluation of sand liquefaction,but also help to gain a better understanding of the seismic resistance design before the construction of the bridge.
In West China,intense earthquakes occur frequently,because of its complex geological and geomorphological conditions,hence the earthquake-induced landslide become one of the most severe seismic hazards there.In this paper a technique for the risk assessment of seismic landslide hazard using GIS approach is developed.The method has been applied to the real case in Longling county,Yunnan Province,where a strong earthquake(M=7.3) which triggered lots of landslides occurred in 1976.With the application of GIS,the relationships between earthquake-induced landslide activity and a number of parameters including lithology,tectonic,site intensity,slope angle,etc.are analyzed.And furthermore,the risk of seismic landslide hazard for this region is assessed using the comprehensive index method.The occurrence of landslide is the result of all factors combination.In the seismic landslide hazard map generated accordingly,it is found that almost all landslides occur in the places which have been grouped as high risk areas. In West China,intense earthquakes occur frequently,because of its complex geological and geomorphological conditions,hence the earthquake-induced landslide become one of the most severe seismic hazards there.In this paper a technique for the risk assessment of seismic landslide hazard using GIS approach is developed.The method has been applied to the real case in Longling county,Yunnan Province,where a strong earthquake(M=7.3) which triggered lots of landslides occurred in 1976.With the application of GIS,the relationships between earthquake-induced landslide activity and a number of parameters including lithology,tectonic,site intensity,slope angle,etc.are analyzed.And furthermore,the risk of seismic landslide hazard for this region is assessed using the comprehensive index method.The occurrence of landslide is the result of all factors combination.In the seismic landslide hazard map generated accordingly,it is found that almost all landslides occur in the places which have been grouped as high risk areas.
With the rapid development of major cities,Subway line has become an important traffic transportation in major cities.A subway line is an important and densely populated lifeline infrastructure.It is difficult to renovate it if a subway line is damaged during earthquake.Therefore,it has become more and more important in ensuring subway safety during earthquake.In this paper,based on the fifth subway line in Beijing,the relationships of ground motion parameters and response spectrums in different site conditions,different risk levels and different depths are discussed.It is determined that the 50 year exceedance probability 63%、10%、2% can be used as the subway earthquake fortification levels.The surface ground motion parameter can be used as the design ground motion parameter.Through studying seismic microzoning and response spectrum characters,this paper defined the earthquake fortification level for the fifth subway line. With the rapid development of major cities,Subway line has become an important traffic transportation in major cities.A subway line is an important and densely populated lifeline infrastructure.It is difficult to renovate it if a subway line is damaged during earthquake.Therefore,it has become more and more important in ensuring subway safety during earthquake.In this paper,based on the fifth subway line in Beijing,the relationships of ground motion parameters and response spectrums in different site conditions,different risk levels and different depths are discussed.It is determined that the 50 year exceedance probability 63%、10%、2% can be used as the subway earthquake fortification levels.The surface ground motion parameter can be used as the design ground motion parameter.Through studying seismic microzoning and response spectrum characters,this paper defined the earthquake fortification level for the fifth subway line.
This paper presents a simple numerical deterministic approach for analysis of stochastic response and dynamic reliability of retaining structures under the stationary random seismic activity.The method is based on general FEM software for structure dynamic analysis.A numerical equivalent unit impulse function is used as an input of seismic load.After the impulse response function of the structure was obtained,a transfer function between the random excitation and response of the structure was adopted to calculate the mean square response and peak response by the Fourier transform.The random seismic response and dynamic reliability of retaining structures including displacement,moment,horizontal and vertical resultant forces on the base,earth pressure along the back of wall are calculated.The results show that Kanai model was more conservative than Ou-Jinping model.Assuming the passage of the response process to a given level as a Markov process was more precise than a Poisson process. This paper presents a simple numerical deterministic approach for analysis of stochastic response and dynamic reliability of retaining structures under the stationary random seismic activity.The method is based on general FEM software for structure dynamic analysis.A numerical equivalent unit impulse function is used as an input of seismic load.After the impulse response function of the structure was obtained,a transfer function between the random excitation and response of the structure was adopted to calculate the mean square response and peak response by the Fourier transform.The random seismic response and dynamic reliability of retaining structures including displacement,moment,horizontal and vertical resultant forces on the base,earth pressure along the back of wall are calculated.The results show that Kanai model was more conservative than Ou-Jinping model.Assuming the passage of the response process to a given level as a Markov process was more precise than a Poisson process.
Based on the simplified structure of rock mass,FLAC~(3D) numerical modeling technique is used to systematically analyze the distribution features of the secondary stress field,strain field and plastic zones in the surrounding rock mass of the underground cavities after the excavation.And the variation characteristics of stress field,strain field and plastic failure zones in the surrounding rock mass of the underground cavities are summarized,which provides basic information and reference for the evaluation of underground cavities stability and project construction. Based on the simplified structure of rock mass,FLAC~(3D) numerical modeling technique is used to systematically analyze the distribution features of the secondary stress field,strain field and plastic zones in the surrounding rock mass of the underground cavities after the excavation.And the variation characteristics of stress field,strain field and plastic failure zones in the surrounding rock mass of the underground cavities are summarized,which provides basic information and reference for the evaluation of underground cavities stability and project construction.
Routine tri-axial CU shear test results indicate the stress-strain relationships of the unsaturated MaLan loess are softening with increasing strain.For practice,an exponential constitutive model with two parameters is derived in this paper.This model can not only describe the stress strain relationship well when the axial strain is less than 15%,but also clearly represent physical behavior by using few parameters that can be easily determined.The results also show that parameters change exponentially with the moisture content and confining pressure. Routine tri-axial CU shear test results indicate the stress-strain relationships of the unsaturated MaLan loess are softening with increasing strain.For practice,an exponential constitutive model with two parameters is derived in this paper.This model can not only describe the stress strain relationship well when the axial strain is less than 15%,but also clearly represent physical behavior by using few parameters that can be easily determined.The results also show that parameters change exponentially with the moisture content and confining pressure.
Loess joints can be generally classified into primary joints,structural joints,weathering joints and unloading joints.Primary joints and structural joints are widespread in northern Shaanxi.Primary joints are widely distributed in Malan loess and are characterized by large density and long stretching.Structural joints,with distinct directivity and spatial difference from region to region,are distributed in Lishi loess.Stability of a highway slope varies with the orientations of loess joints.When the joints have their orientations similar to that of the slope,they can have the maximum effect to reduce slope stability.The vertical joints have less efect.When joints are perpendicular or intersect the slope,their effects are minor..Several sets of joints can form some regular discontinuity patterns on slope surfaces.In the three dimensional space,they can form the tabular,sphenoid,and columnar structure patterns.The structural bodies with different forms have different effects on the stability of slopes.The authors also discuss the method of calculating the stability of slopes with oblique joints. Loess joints can be generally classified into primary joints,structural joints,weathering joints and unloading joints.Primary joints and structural joints are widespread in northern Shaanxi.Primary joints are widely distributed in Malan loess and are characterized by large density and long stretching.Structural joints,with distinct directivity and spatial difference from region to region,are distributed in Lishi loess.Stability of a highway slope varies with the orientations of loess joints.When the joints have their orientations similar to that of the slope,they can have the maximum effect to reduce slope stability.The vertical joints have less efect.When joints are perpendicular or intersect the slope,their effects are minor..Several sets of joints can form some regular discontinuity patterns on slope surfaces.In the three dimensional space,they can form the tabular,sphenoid,and columnar structure patterns.The structural bodies with different forms have different effects on the stability of slopes.The authors also discuss the method of calculating the stability of slopes with oblique joints.
Highly wetted loess is a kind of loess with high water content,degree of saturation and compressibility.Its mechanical strength decreases apparently when water seeps in.Its mechanical property varies with the water content,which will influence the project construction.In this paper,on the basis of several kinds of in-situ testing and the construction of gravel pile composite foundation in highly wetted loess subgrade treatment in an express way project,the strength and deformation of the subgrade before and after treatment are analyzed,the mechanical properties of the highly wetted loess are further studied.Finally the applicability of various construction technology of gravel pile composite foundation treatment in highly wetted loess as well as the key points in foundation treatment are discussed.The presented results are good reference for similar engineering practice. Highly wetted loess is a kind of loess with high water content,degree of saturation and compressibility.Its mechanical strength decreases apparently when water seeps in.Its mechanical property varies with the water content,which will influence the project construction.In this paper,on the basis of several kinds of in-situ testing and the construction of gravel pile composite foundation in highly wetted loess subgrade treatment in an express way project,the strength and deformation of the subgrade before and after treatment are analyzed,the mechanical properties of the highly wetted loess are further studied.Finally the applicability of various construction technology of gravel pile composite foundation treatment in highly wetted loess as well as the key points in foundation treatment are discussed.The presented results are good reference for similar engineering practice.
With the development of underground structures in Shanghai,the ground freezing method is more and more widely used in tunnel construction(such as the soil reinforcement of the passway and pumping house of tunnels). Therefore,it becomes important to develop guidelines for appropriate applications of such technology in Shanghai.This paper presents results of the instantaneous uniaxial compressive strength,which is one of the important parameters for design of the frozen wall.Lab tests were conducted on sap green ~ grass-yellow silty clay and grass-yellow mealy sand which were often encountered in the tunnel passway construction in Shanghai.The relationship between the compressive strength and temperature of two kinds of frozen soils were obtained.Effects of the temperature and water contents on the relationship were also evaluated. With the development of underground structures in Shanghai,the ground freezing method is more and more widely used in tunnel construction(such as the soil reinforcement of the passway and pumping house of tunnels). Therefore,it becomes important to develop guidelines for appropriate applications of such technology in Shanghai.This paper presents results of the instantaneous uniaxial compressive strength,which is one of the important parameters for design of the frozen wall.Lab tests were conducted on sap green ~ grass-yellow silty clay and grass-yellow mealy sand which were often encountered in the tunnel passway construction in Shanghai.The relationship between the compressive strength and temperature of two kinds of frozen soils were obtained.Effects of the temperature and water contents on the relationship were also evaluated.
Through the conventional laboratory testing of saline soil samples collected from twelve different places(Kashi,Sinkiang,P.R.China), the representative crude saline soil samples were selected for the experiment of freezing and thawing cycles in open systems.Moving patterns of water and solute migration and variations of shear strength of the representative crude saline soils were studied for different kinds of soils.The result of the tests shows that moving patterns of water and solute in low liquid limit clay under several freezing and thawing cycles are generally consistent with water and solute migrating upwards.The distribution of cohesion of low liquid limit clay decreases linearly form bottom to top and the distribution of the internal friction angle is in s-shape.Both the water and the solute in low liquid limit clay with sand move to the cold end under freezing and thawing cycles and the profile of ion indicates higher concentration in middle than in both ends.The distribution of cohesion of low liquid limit clay with sand is in reverse s-shape,while the distribution of internal friction angle is in s-shape. Through the conventional laboratory testing of saline soil samples collected from twelve different places(Kashi,Sinkiang,P.R.China), the representative crude saline soil samples were selected for the experiment of freezing and thawing cycles in open systems.Moving patterns of water and solute migration and variations of shear strength of the representative crude saline soils were studied for different kinds of soils.The result of the tests shows that moving patterns of water and solute in low liquid limit clay under several freezing and thawing cycles are generally consistent with water and solute migrating upwards.The distribution of cohesion of low liquid limit clay decreases linearly form bottom to top and the distribution of the internal friction angle is in s-shape.Both the water and the solute in low liquid limit clay with sand move to the cold end under freezing and thawing cycles and the profile of ion indicates higher concentration in middle than in both ends.The distribution of cohesion of low liquid limit clay with sand is in reverse s-shape,while the distribution of internal friction angle is in s-shape.
Aimed to address the expansive soil problem in highway construction in the centre of Anhui Province,typical soil specimens from the He-Liu-Ye expressway are chosen to carry out systematically experiments to study the characteristics of California Bearing Ratio(CBR) of expansive soils,and based on this the usability of expansive soils as subgrade materials is discussed.The research shows:(1)The initial water content affects the CBR value markedly,and the initial water content corresponding to the maximum CBR value is high than the optimal initial water content,and the discrepancy grows with the compaction work;(2)The CBR swell amount reduces when the initial water content increases.The CBR swell amount is higher as the initial water content is lower,and the roadbed water-stability is worse;(3)The optimal initial water content is lower when the compaction work is greater,and the range of variable water content suitable to pad is wider.So the heavy compaction standard is suggested in the site construction control;(4) In the condition of heavy compaction standard,the low-class expansive soil can meet both the compactioness request and the CBR request to pad the bottom of embankment,the middle-class expansive soil must be treated as roadbed padding materials.The results of the research could be referred to the construction of expressway in the expansive soil areas. Aimed to address the expansive soil problem in highway construction in the centre of Anhui Province,typical soil specimens from the He-Liu-Ye expressway are chosen to carry out systematically experiments to study the characteristics of California Bearing Ratio(CBR) of expansive soils,and based on this the usability of expansive soils as subgrade materials is discussed.The research shows:(1)The initial water content affects the CBR value markedly,and the initial water content corresponding to the maximum CBR value is high than the optimal initial water content,and the discrepancy grows with the compaction work;(2)The CBR swell amount reduces when the initial water content increases.The CBR swell amount is higher as the initial water content is lower,and the roadbed water-stability is worse;(3)The optimal initial water content is lower when the compaction work is greater,and the range of variable water content suitable to pad is wider.So the heavy compaction standard is suggested in the site construction control;(4) In the condition of heavy compaction standard,the low-class expansive soil can meet both the compactioness request and the CBR request to pad the bottom of embankment,the middle-class expansive soil must be treated as roadbed padding materials.The results of the research could be referred to the construction of expressway in the expansive soil areas.
This paper presents a case study of an impact technology applied in a highway embankment on collapsible loess.Based on soil test and settlement observation,the authors assessed physical and mechanical parameters of subgrade(collapsibility,dry density,void ratio,compression modulus,settlement and other parameters) and their changes with the depth of soil strata and the pressing number before and after the impact compaction..The results show that the physical and mechnical properties of soil were improved greatly by the compaction.The overall strength of highway subgrade can be enhanced.It is concluded that the impact compaction technology is effective and practical for treatment of collapsible loess subgrade. This paper presents a case study of an impact technology applied in a highway embankment on collapsible loess.Based on soil test and settlement observation,the authors assessed physical and mechanical parameters of subgrade(collapsibility,dry density,void ratio,compression modulus,settlement and other parameters) and their changes with the depth of soil strata and the pressing number before and after the impact compaction..The results show that the physical and mechnical properties of soil were improved greatly by the compaction.The overall strength of highway subgrade can be enhanced.It is concluded that the impact compaction technology is effective and practical for treatment of collapsible loess subgrade.
The Elman network has characteristics of dynamic adaptation,quick convergence and high accuracy.With the consideration of the basic feature of the settlement of soft ground,an Elman network model for predicting the settlement of soft ground is established.Considering the limitation of classical BP algorithm,modified BP algorithm is used to train the network.Through application in real case,the model of the Elman network presented in this paper is proved to be reliable and applicable. The Elman network has characteristics of dynamic adaptation,quick convergence and high accuracy.With the consideration of the basic feature of the settlement of soft ground,an Elman network model for predicting the settlement of soft ground is established.Considering the limitation of classical BP algorithm,modified BP algorithm is used to train the network.Through application in real case,the model of the Elman network presented in this paper is proved to be reliable and applicable.
The ground settlement caused by large-scale urban construction has become a new restriction factor of ground settlement in soft soil area of Shanghai.An unequal time-interval GM(1,1) predicting grey model is established according to the characteristics of ground settlement in soft soil area.The model is proved to be satisfying through the examination of engineering practice,and is of significant importance for the prediction and control of ground settlement.induced by engineering construction. The ground settlement caused by large-scale urban construction has become a new restriction factor of ground settlement in soft soil area of Shanghai.An unequal time-interval GM(1,1) predicting grey model is established according to the characteristics of ground settlement in soft soil area.The model is proved to be satisfying through the examination of engineering practice,and is of significant importance for the prediction and control of ground settlement.induced by engineering construction.
The Shuping Landslide of the Changjiang River was continuously monitored by using the automatic displacement meters for almost one year. The results show that the controlling factors of the shuping Landslide displacement are rainfall and water fluctuation.And currently the velocity of slope displacement is small,which will not cause slope instability.Through the continuous data recording of the automatic displacement meters,the deformation characteristics of Shuping landslide body are accurately reflected.In addition,the data acquisition process is simple,hence it is appropriate to apply this system to the slope monitoring of the Three Gorges reservoir. The Shuping Landslide of the Changjiang River was continuously monitored by using the automatic displacement meters for almost one year. The results show that the controlling factors of the shuping Landslide displacement are rainfall and water fluctuation.And currently the velocity of slope displacement is small,which will not cause slope instability.Through the continuous data recording of the automatic displacement meters,the deformation characteristics of Shuping landslide body are accurately reflected.In addition,the data acquisition process is simple,hence it is appropriate to apply this system to the slope monitoring of the Three Gorges reservoir.
Two neighbor tall buildings are constructed on soft soil ground.The piles of the buildings are subject to deflection due to excavation-induced soil movement.Based on the project,three-dimensional finite-difference program is applied to calculate the deflection of piles due to the soil lateral movements.The effects of pit excavation on pile deflection have also been studied. Two neighbor tall buildings are constructed on soft soil ground.The piles of the buildings are subject to deflection due to excavation-induced soil movement.Based on the project,three-dimensional finite-difference program is applied to calculate the deflection of piles due to the soil lateral movements.The effects of pit excavation on pile deflection have also been studied.
In this paper,the authors analyze internal forces of a soil nail system during excavation using FLAC3D.Based on excavation and supporting conditions of soil nail structures,the internal force distribution patterns weredetermined.In addition,axial force and shear stress of the soil nail were evaluated.The experimental data matchwell with the computational results from FLAC3D,which allows one to gain a better understanding of interaction ofnails and soil. In this paper,the authors analyze internal forces of a soil nail system during excavation using FLAC3D.Based on excavation and supporting conditions of soil nail structures,the internal force distribution patterns weredetermined.In addition,axial force and shear stress of the soil nail were evaluated.The experimental data matchwell with the computational results from FLAC3D,which allows one to gain a better understanding of interaction ofnails and soil.
The dam foundation of Xiabandi Hydro-junctionin Xinjiang,which is about 147.95m thick,is a typical deep-thick overburden deposit.Its mainly composed of glacio-fluvial deposit layers,alluvial-diluvial soil and gravel,soil lens.The structure is very complicated.In order to find a a appropriate construction technology of curtain grouting to prevent dam foundation seepage,a specific in-situ test process related to deep overburden of dam foundation was carried out.Through the experiment,the grout materal,mixture proportion,construction measures and parameter have been analyzed in detail. The dam foundation of Xiabandi Hydro-junctionin Xinjiang,which is about 147.95m thick,is a typical deep-thick overburden deposit.Its mainly composed of glacio-fluvial deposit layers,alluvial-diluvial soil and gravel,soil lens.The structure is very complicated.In order to find a a appropriate construction technology of curtain grouting to prevent dam foundation seepage,a specific in-situ test process related to deep overburden of dam foundation was carried out.Through the experiment,the grout materal,mixture proportion,construction measures and parameter have been analyzed in detail.
The dredger fill is formed under the hydraulic filling,which consists of fine particles and has a poor consolidation capability.Its natural sedimentation and consolidation after dredger filling is a very slow process,and only when the surface duricrust has formed,the ground improvement can be started.So it is urgently necessary to accelerate the consolidation process,and transform the dredged mud into a solid ground which has a certain bearing capacity.Laboratory model tests were carried out to simulate the effect of consolidation agent.Lime and cement were chosen as the consolidation agents to be added into the dredger fill to accelerate the consolidation process respectively.The solidifying mechanism and consolidation performance of the two materials have been studied carefully.The reason for their different consolidation behavior is tentatively concluded,and the consolidation mechanism is correspondingly put forward.A more economical and feasible method for consolidating foundation of dredger fill has been provided in this paper. The dredger fill is formed under the hydraulic filling,which consists of fine particles and has a poor consolidation capability.Its natural sedimentation and consolidation after dredger filling is a very slow process,and only when the surface duricrust has formed,the ground improvement can be started.So it is urgently necessary to accelerate the consolidation process,and transform the dredged mud into a solid ground which has a certain bearing capacity.Laboratory model tests were carried out to simulate the effect of consolidation agent.Lime and cement were chosen as the consolidation agents to be added into the dredger fill to accelerate the consolidation process respectively.The solidifying mechanism and consolidation performance of the two materials have been studied carefully.The reason for their different consolidation behavior is tentatively concluded,and the consolidation mechanism is correspondingly put forward.A more economical and feasible method for consolidating foundation of dredger fill has been provided in this paper.